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SubjectRe: [PATCH 1/3] perf tool: precise mode requires exclude_guest
On 12.09.12 09:16:28, David Ahern wrote:
> Summary of events per Peter:
>
> "Intel PEBS in VT-x context uses the DS address as a guest linear address,
> even though its programmed by the host as a host linear address. This
> either results in guest memory corruption and or the hardware faulting and
> 'crashing' the virtual machine. Therefore we have to disable PEBS on VT-x
> enter and re-enable on VT-x exit, enforcing a strict exclude_guest.
>
> AMB IBS does work but doesn't currently support exclude_* at all,
> setting an exclude_* bit will make it fail."
>
> This patch handles userspace perf command, setting the exclude_guest
> attribute if precise mode is requested, but only if a user has not
> specified a request for guest or host only profiling (G or H attribute).
>
> Kernel side AMD currently ignores all exclude_* bits, so there is no impact
> to existing IBS code paths. Robert Richter has a patch where IBS code will
> return EINVAL if an exclude_* bit is set. When this goes in it means use
> of :p on AMD with IBS will first fail with EINVAL (because exclude_guest
> will be set). Then the existing fallback code within perf will unset
> exclude_guest and try again. The second attempt will succeed if the CPU
> supports IBS profiling.
>
> Signed-off-by: David Ahern <dsahern@gmail.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Robert Richter <robert.richter@amd.com>
> Cc: Gleb Natapov <gleb@redhat.com>
> Cc: Avi Kivity <avi@redhat.com>
> Link: https://lkml.org/lkml/2012/7/9/264
> ---
> tools/perf/util/parse-events.c | 3 +++
> 1 file changed, 3 insertions(+)

Acked-by: Robert Richter <robert.richter@amd.com>

I tested the patch set with AMD IBS and it works fine.

-Robert

>
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 44afcf4..696cc7e 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -694,6 +694,9 @@ static int get_event_modifier(struct event_modifier *mod, char *str,
> eH = 0;
> } else if (*str == 'p') {
> precise++;
> + /* use of precise requires exclude_guest */
> + if (!exclude_GH)
> + eG = 1;
> } else
> break;
>
> --
> 1.7.10.1
>
>

--
Advanced Micro Devices, Inc.
Operating System Research Center



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